A backdoor is an undocumented method of gaining access to program or a computer by using another installed program or rootkit that bypasses normal authentication. The backdoor is generally written by the programmer who created the original program and is often only known to that person. Using backdoors are an effective way to regain access to a computer that the intruders have already compromised. They can often bypass security measures such as firewalls, password protection and intrusion detection systems. Backdoors are installed on one’s computer by attaching themselves to one of the over 65,000 ports computers have for internet communication. The intruder sets up a backdoor (also called a “server”) and has it “listen” for incoming connections on a specific port. They then use a “client” to tell the server backdoor that they are going to enter the machine. The server then welcomes them in, bypassing the computer’s security.
Because many of these backdoors are also viruses, worms and other malware, antivirus software is always identifying new backdoors that can be removed from a client’s system. You can avoid vulnerability to backdoors by running quality antivirus software, maintaining updates to your operating system and other installed software and by using caution when you open email attachments, even when it looks like it’s from someone you know. It’s also a good idea to use your antivirus tools to scan all attachments & downloads before opening them.